Plaster of Paris casts have been in use to immobilize body members or limbs for some time. The plaster of Paris bandages have been supplemented and, to some extent, superseded by synthetic cast tapes or bandages which employ polymeric materials on a substrate. The polymeric materials have been cured by exposure to ultra violet light or contained polymers which would cure when reacted with water. Examples of the ultra violet light cured cast can be found in U.S. Pat. No. 3,881,473. More recently, water-cured or water-reactive polyurethane compositions have been used in forming orthopedic casts and the polyurethane materials have largely supplanted other polymeric synthetic casting materials. The polyurethane casting materials are of the type which are disclosed in U.S. Pat. Nos. 4,376,438 and 4,411,262.
The fibrous substrate used in the synthetic casting materials has become, to a large extent, a fiberglass material. The fiberglass materials offer advantages in terms of strength of the finished cast and various constructions of fiberglass fabrics have been used for the substrates for the synthetic casting tapes. The patents mentioned above disclose the use of different fiberglass materials as the substrate for casting tapes. In addition U.S. Pat. Nos. 3,686,725, 3,787,272 and 3,882,857 disclose specific fiberglass materials, or the treatment of fiberglass materials, to produce fiberglass substrates which are particularly suitable for use in orthopedic casts.
U.S. Pat. No. 4,323,061 discloses a cast substrate made from a combination of glass fibers and a second fiber such as cotton, flax, rayon, wool, acrylic resin, nylon, Teflon or polyester. The purpose of the second fiber in the substrate is to hold the curable resin on the substrate.
U.S. Pat. No. 3,332,416 discloses a plaster of Paris cast bandage with a woven substrate made with a combination of elastic and inelastic fibers.
Although fiberglass has been extensively used as a substrate material in orthopedic casts, with different reactive polymers, all of these casting materials suffer certain disadvantages. One of the major disadvantages is the conformability of the casting tape to the body of the patient. Conformability is the characteristic of the casting tape which has been defined as that property which describes the ability of the bandage or casting tape to adapt to or intimately lay down against the compound curves and protrusions of a body member. Fiberglass casting tapes are generally stiffer than casting tapes made of other fibers, and cast technicians and surgeons have some difficulty conforming the fiberglass casting tapes to the limbs of a patient. For this reason, the originally developed fiberglass casting tapes were used, to a large extent, for secondary casting. A secondary cast is a cast which is applied to a patient approximately seven to ten days after the initial cast has been applied. A primary cast is applied to the patient at the time the broken bone in the limb is set. Because of the greater conformability of plaster of Paris cast bandages, plaster of Paris has been employed as a primary casting material. Usually, when the secondary cast is applied, the casting material of choice would be a synthetic cast because of its lighter weight and ability to resist moisture, as compared to plaster of Paris. Also, the conformability is not as critical in a secondary cast as it is in a primary cast. Although the more recently introduced fiberglass casting tapes have greater conformability than the original fiberglass casting tapes, these tapes are still not as conformable as plaster of Paris bandages.